I. Field of the Invention
The present invention relates generally to power converters and, more particularly, to a DC-DC switching power converter.
II. Description of Related Art
There are many types of previously known power supplies. One type of previously known power supply is a linear power supply which utilizes a transformer to convert the voltage from one level to another level. Such linear power supplies are advantageous since the range of conversion, both up and down, of the voltage from the power source and to the load may be varied over an almost infinite range. A disadvantage of the previously known linear power supplies, however, is that they require a large and heavy transformer for the conversion. As such, such linear power supplies are ill suited for many applications, such as small electronic devices, cellular phones, etc. A still further disadvantage of the previously known linear power supplies is that they are relatively inefficient in operation and dissipate heat due to that inefficiency.
There have, however, been previously known switching power supplies which do not require a transformer for the voltage conversion between the source and the load. Such switching power supplies, also known as boost converters, utilize a voltage storage device, such as an inductor, which is charged at a high frequency rate and, when charged to the desired voltage, discharge it to the load. Furthermore, in order to change the output voltage ultimately discharged to the load, a switch control circuit changes the frequency at which the energy storage device is charged to thereby vary the output voltage to the load.
In one type of previously known power converter, a transmission line is used to store the electrical power which is ultimately discharged to the load. In these previously known converters, a power source is selectively connected through a first switch to one end of the transmission line while the second end of the transmission line is terminated, typically by ground. A second switch then selectively electrically connects the other end of the transmission line to the load.
In operation, the first switch is opened and closed at a sufficiently high frequency to generate a wave signal through the transmission line. The transmission line terminates in an impedance mismatch so that the wave generated in the transmission line propagates between the ends of the transmission line thus increasing the amount of power stored within the transmission line. Ultimately, with the first switch in an open position, the second switch is closed thus applying the power accumulated to the load at a voltage level higher than the voltage source.
In order to vary the voltage gain of the power converter, the switch frequency of the second switch, which electrically connects the transmission line to the load when closed, is varied. Consequently, if the propagating wave in the transmission line has less time to accumulate, the amount of accumulated charge changes thus reducing the output voltage. Conversely, if the propagating wave has more time to accumulate within the transmission line, the amount of accumulated charge increases, thus increasing the output voltage applied to the load.
These types of previously known DC-DC converters utilizing a transmission line as the energy storage device, however, suffer from several major disadvantages. One disadvantage is that, since the generating signals to control the switching frequency of the second switch may vary over a wide range, the complexity of the circuitry of the switch control likewise increases. This may also increase the number of discrete passive components which can significantly increase the overall size of the system and render the DC-DC converter unusable for small electronic devices.